Uranium alkoxy compoundsand method



United States Patent Ofi ice 2,735,857 Patented Feb. 21, 1956 URANIUMALKOXY COMPOUNDS AND METHOD OF PREPARING SAME Application October 17,1944, Serial No. 559,124

20 Claims. (Cl. 260429.1)

No Drawing.

This invention relates to compounds of uranium and their preparation,particularly to the alkoxy compounds of uranium which have been found tobe especially useful.

In order to separate the isotopes of uranium by diffusion methods,uranium compounds are employed. If these compounds are to be useful fortheir intended purpose it is desirable that they be liquid at ordinarytemperatures, that they undergo no substantial thermal de compositionnor have corrosive action on conventional construction materials, andthat they have an appreciable vapor pressure in the temperature zone of100 C. to 200 C.

We have discovered that certain of the alkoxides of uranium have thecharacteristics noted above and that they may therefore be convenientlyemployed in the separation of uranium isotopes. Those compounds whichare considered particularly useful for the above purpose are the tetra-,penta-, and hexa-alkoxides of uranium wherein the alkoxy radical isselected from the group consisting of the methoxy, ethoxy, propoxy, andbutoxy radicals. Moreover other alkoxy derivatives of uranium andmonovalent alkoxy radicals such as allyloxy methallyloxy derivatives orthe corresponding derivatives of other monovalent aliphatic alcoholssuch as hexyl or lauryl alcohol and similar alcohols were foundoperative. in general such compounds have the probable structure U(OR)where R is a monovalent aliphatic radical and x is a small whole numberfrom 4 to 6.

It is thus an object of the present invention to provide methods forproducing alkoxy compounds of uranium particularly the tetra-, pentaandhexa-alkoxides of uranium wherein the alkoxy radical is selected fromthe group consisting of the methoxy, ethoxy, propoxy, and butoxyradicals.

Another object of the present invention is the provision of new anduseful uranium compounds, such as, uranium tetraalkoxides, uraniumpenta-alkoxides, uranium. hexaalkoxides and addition, substitution, andinterconversion compounds of the uranium penta-alkoxides.

Another and still further object of the present invention is theproduction of uranium tetraethoxide, uranium pentaethoxide, uraniumhexaethoxide and addition, substitution, and interconversion compoundsof uranium pentaethoxide.

Other objects and many of the attendant advantages of the presentinvention will be appreciated as the same becomes better understood byreference to the following description.

We have found that a uranium tetra-alkoxide such as the methoxy, ethoxy,propoxy or butoxy uranium compounds can be converted to a uraniumpenta-alkoxide of the same radical group by oxidizing the tetra-alkoxideunder appropriate conditions.

The first step in the method of producing a uranium penta-alkoxide or auranium hexa-alkoxide of the abovementioned alkoxy group is theformation of a uranium tetra-alkoxide of said group by the substitutionof uranium for the alkali metal of an alkali alkoxide of the t methoxy,ethoxy, propoxy, and butoxy radical group. The uranium tetra-alkoxide soproduced is converted to uranium penta-alkoxide in a further step byoxidizing the uranium to a pentavalent state and introducing anadditional alkoxy radical into the compound. This may be done byintroducing oxygen either as elemental oxygen or by a peroxide such asbenzoyl peroxide, or acetyl peroxide into a uranium tetra-alkoxidesuspension in an alcohol having the same alkyl radical as that of theuranium tetra-alkoxide, or by introducing bromine followed by an alkalialkoxide having the same alkyl radical as that of the uraniumtetra-alkoxide.

The production of a uranium hexa-alkoxide of the above-mentioned alkoxygroup from a uranium pentaalkoxide of the same radical group is achievedthrough the intermediate of a novel addition compound. It is possible toproduce this addition complex or compound of a uranium penta-alkoxide byadding the uranium penta-alkoxide to a solution of an alkali alkoxide inalcohol under an inert atmosphere in which the alkali alkoxide has thesame alkoxy radical and the alcohol the same alkyl radical as thepenta-alkoxide. The addition compound of uranium penta-alkoxide and thealkali metal alcoholate thus formed is then converted to uraniumhexa-alkoxide by oxidation.

In practicing the method of the present invention We first prepare acompound of a uranium tetra-alkoxide, such as uranium tetraethoxide,from an alkali alkoxide alcohol solution, such as sodium ethoxideethanol solution, by addiing a uranium tetrahalide, such as uraniumtetrachloride or tetrabromide to the solution while agitating the same.It is to be emphasized that an alkoxide of any of the alkali metals maybe employed with other alkoxy radicals such as the methoxy, ethoxy,propoxy, and butoxy radicals. Also other tetrahalides such as thebromides, iodides and fluorides are suitable.

A reaction takes place with evolution of heat producing a uraniumtetra-alkoxide, such as uranium tetraethoxide and the correspondingalkali metal halides. If the uranium tetraalkoxide alone is desired thealcohol may first be distilled off in any suitable manner and theresidue subjected to fractional distillation at a reduced pressure toremove other substances leaving uranium tetraalkoxide. If it is notdesired to isolate the uranium tetraalkoxide, the solution containingthe uranium tetraalkoxide is next oxidized by introducing oxygen intothe reaction mixture, the oxidation resulting in the attachment of afifth alkoxy radical to the uranium, thus producing a uraniumpenta-alkoxide, such as uranium pentaethoxide. The bulk of the alcoholis next distilled off under nitrogen at atmospheric pressure followed byfurther distillation under vacuum to remove the last traces of alcohol.Finally, the uranium penta-alkoxide is purified by distillation under ahigh vacuum leaving a residue including an alkali halide.

The sixth alkoxy radical of uranium hexa-alkoxide, as previously noted,is attached to the uranium through the use of a novel intermediateaddition compound of a uranium penta-alkoxide, such as uraniumpentaethoxide. This addition compound is first formed by reacting theuranium penta-alkoxide with an alkali alkoxide alcohol solution, such asa sodium ethoxide ethanol solution, under an inert atmosphere. A uraniumhexa-alkoxide, such as uranium hexaethoxide, is then produced from theaddition compound by oxidation with any suitable oxidizing agent, suchas acetyl or benzoyl peroxide. The major portion of the alcohol is thendistilled off under an inert atmosphere at atmospheric pressure followedby a further distillation under vacuum to remove the last traces ofalcohol. The uranium hexa-alkoxide so obtained is finally purified byfractionating at a low pressure leaving a residue including analkali-benzoate or an alkali acetate.

Solid and liquid compounds'are secured. In general the tetraalkoxyderivatives are solids whicharedifiicultly soluble or insoluble inorganicsolvents. On the other hand many of the penta and hexaderivatives, particularly the -alkoxidcs corresponding to the loweraliphatic alcohols are generally liquids.

Example] Aspecific example of the methodof producinga uraniumpenta-alkoxide, such as uraniumpentaethoxide, in "accordance withthe-present invention is as follows: 800

cc. of dry ethanol prepared in anyconvenientmanner is placed in asuitable container equipped with an agitator and a reflux condenser. 46grams (2 gram atoms) of sodium metal is then. reacted with the alcoholby adding the sodium in small amounts at such a rate that the reactiondoesnot get outofcontrol. In order to protect the sodium ethoxide formedby the reaction from undesirable oxidation and moisture when theevolution of hydrogen resulting from the reaction isnot sufficientlyrapid, an atmosphere of dry inert gas such as nitrogen is maintainedover the contents of the container. When the sodium has completelyreacted, the container and contents are cooled, preferably to roomtemperature.

The cooled sodium ethoxide solution is now stirred rapidly while a totalof 190 grams (0.5 mole) of powdered anhydrous UCli, prepared in anysuitablemanner, is added in 20-gram portions at intervals'of aboutminutes in the presence of an atmosphere of dry nitrogen, inasmuch assodium ethoxide and uranium ethoxide are sensitive to oxygen andmoisture. If desired, the reaction may be carried out in an atmosphereofdry air instead of nitrogen if it is carried out quickly and in aclosed vessel. Since the reaction of uranium tetrachloride with analcoholic solution of sodium ethoxide is exothermic, it may be necessaryto cool the reaction vessel during the addition of the uraniumtetrachloride if the alcohol boils too vigorously. 'When the heat of thereaction is no longer sufiicient to cause the reaction mixture toreflux, external The reaction above results in the formation oftheuranium tetraethoxide in accordance with the following equation:

If desired theuranium tetraethoxide may be recovered by distillation ofthe excess alcohol. This compound is a light green solid which does notdistill at atmospheric pressure. It is insoluble in the common organicsolvents such as acetone, or chloroform and is very susceptible tohydrolysis. -Uranium pentaethoxide is generally made from the reactionmixture-secured by the above process without attempting to recover the'tetraethoxy compound. In such a case, after cooling the reactionmixture, the nitrogen in the container is first evacuated; and 2.5liters (0.1 mole) of dry oxygen is then slowly admitted to thecontainer, while vigorous stirring is maintained. As the oxygen isabsorbed by the reaction mixture, the mixture warms up and changes colorfrom a light green to a dark brown. After all of the oxygen has beenpassed into the container, nitrogen is readmitted and stirring iscontinued for another 30 minutes. The foregoing reaction results in theproduction of uranium pen'taethoxide in accordance with the followingequation:

The bulk of the alcohol in the reaction mixture is now distilled offunder a streamof nitrogen at atmospheric pressure while suitablystirring the mixture. The heating to effect the distillation ispreferably accomplished by immersing the container in an oil bath andgradually raising the temperature of the bath to C. When the darkresidue appears to be nearly free of alcohol, the container with itscontents is cooled, the nitrogen stream is shut off and the container isevacuated by suitable means.

The distillation is now continued at a, pressure of 15 to 20mm. of Hg byrewarming the oil bath gradually to 150 C. in order to remove more ofthe alcohol. The pressure in the system is now reduced to 1 to 3 mm. ofHg taking care in doing so to prevent violent boiling of the contents ofthe container. Heating with the oil bath at a temperature of 150 C. isnow continued for an hour to remove the last traces of alcohol. a

In order to separate the uranium pcntaethoxide from the large quantitiesof sodium chloride and by-products of the reaction mixture, the brownalmost solid residue in thecontainer is now heated under a vacuum todistill off the uranium pentaethoxide. To the accomplishment of thisenda clean receiver is attached to the outlet end of 'the container. Thesystem is'evacuated to a pressure of .001.004 mm; of Hg and thetemperature of the oil bath is-gradually raised to 200 C., therebycausing distillation of the uraniumpentaethoxide. After the'distillationhas started, the temperature-of the oil bath may be lowered to (3.,without decreasing the distillation. Toward the end of the reaction, thetemperature of the oil bath may be raised to and maintained at 240 C.until the distillation ceases. The distillation of uranium pentaethoxidebegins at a bath temperature of about 180 C.

About 151 grams (0.326 mole) of quite pure uranium pentaethoxide isobtained'which represents a yield of 65 per cent based on the amount ofUCl4 used. While this product, as stated, is quite pure it may befurther fractionated by'redistillation at 0.002 mm. of Hg pressure. Thecompound obtained is a dark brown liquid which has 'a compositioncorresponding to the formula U(OC2H5)5 and distills at 122123 C. at apressure of 0.001 mm. of mercury and has a density d4 1.70. it issoluble in organic solvents such as benzene, acetone and chloroform andis susceptible tohydrolysis. Upon exposure to oxygen -it oxidizes tothered liquid U(OC2H5)6. Other alkoxy types may be prepared in accordancewith this process. For example, the n'-propyl derivative may be preparedby substituting n-propanol for ethyl alcohol. In such a case a similarcompound somewhat less stable is secured. In like manner similarcompounds may be prepared fromn-butyl or tertiary butyl alcohol.

Example 11 A. specific exampleof the. method of producing a uraniumhexa-alkoxide, such as uranium hexaethoxide, in accordance with thepresent invention is as follows: In a suitable container, designed toenable one to work in an-atmosphere of nitrogen-or other inert gas, isplaced 300 milliliters of'dry ethanol and to this is added 1.69 grams(0.0735 gram atom) of sodium. After the sodium has reacted with theethanol and the solution has been cooled in an atmosphere of. nitrogen,20 milliliters (34 grams, 0.0735 mole). of uranium pentaethoxide isadded. Upon stirring this mixture the dark brown color of pentaethoxidedisappears and a clear light green solution of thecompound NaU(OC2H5)sis formed. The foregoing reaction-results in the production of anaddition compound in accordance with the following equation:

U OCzHs) 5 NaOCzHs- NaU OCzHs) s Throughout'this.preparation.anatmosphere of dry nitrogen must. bemaintained because uranium hexaethox-.idezis-sensitiveato air a1'1d highly.sensitive'to moisture.

. Tothetforegoing.solution, which is very rapidly stirred, -8z90 grams(0.036? mole) of dry powdered-benzoylperoxide is added. The mixturequickly turns dark red with the liberation of some heat, and agelatinous precipitate of sodium benzoate appears. The'mixture israpidly stirred at room temperature under an atmosphere of dry nitrogenfor about an hour. The foregoing reaction results in the formation ofuranium hexaethoxide in accordance with the following equation:

At the end of the period of stirring the major portion of the ethanol isdistilled off with stirring under a stream of nitrogen at atmosphericpressure by heating the container in an oil bath at 110 C. afterconnecting it to a suitable receiver. The container is now evacuated toa pressure of to mm. of Hg and more of the alcohol removed by graduallyraising the temperature of the oil bath surrounding the container to 115C. The remainder of the alcohol is removed by evacuating to aboutOJS mm.and heating at approximately 100 C. for about 15 minutes.

After cooling and replacing the alcohol receiver with a clean dryreceiver, the container is evacuated to a pressure of 0.002 to 0.003 mm.of Hg and the distillation of the uranium hexaethoxide is carried out byheating with an oil bath at a temperature of 140 C. as long as any ofthe red liquid comes over. While the temperature of 140 C. is preferredbecause the distillation can be carried out quicker and more completely,the uranium hexaethoxide may alternatively be distilled slowly from thereaction mixture at a temperature of 90 to 100 C.

The yield of crude uranium hexaethoxide is about 20 grams. This materialmay be further fractionated at a pressure of about 0.001 mm. of Hg inorder to separate impurities such as ethyl benzoate and uraniumpentaethoxide. The yield is about 16 grams of substantially pure liquid,uranium hexaethoxide, which is' darker red and has a boiling point of 72to 74 C. at a pressure of 0.001 mm. of Hg. The method gives about 43 percent yield based on the uranium pentaethoxide used. This compound hasdensity d4 1.55 and is very soluble in all common organic solvents. Thecorresponding npropyl, n-butyl, isobutyl, isopropyl, tertiary butyl oramyl derivatives may be made in similar manner.

Example III Another example of the method of producing a uraniumpentaalkoxide, such as uranium penta-n-propoxide is as follows. In theapparatus used for the preparation of uranium pentaethoxide was placed150 cc. of dry propanol and 5.75 g. (0.25 g. atom) of finely cut sodium.When all of the sodium was in solution, 23.75 g. (0.0625 mole) ofuranium tetrachloride was added in small portions. A green suspensionresulted. The mixture was stirred and gently warmed for one hour. Afterthe suspension had cooled to room temperature, a solution of 1.58 cc.(0.0625 g. atom) of bromine in 10 cc. of dry benzene was added dropwise.The reaction mixture became dark brown in color. After five minutes, asolution of 0.0625 mole of sodium propoxide in 75 cc. of anhydrouspropanol was added quickly. A lighter gray color resulted and stirringwas continued one hour.

The suspension was concentrated into a 200 cc. Claisen fiask and theproduct was distilled with a mercury ditfusion pump. The uraniumpenta-n-propoxide obtained distilled at 180l85/0.009 mm., and weighed 16g. (48.1%). On redistillation there was obtained 13.8 g. (41.5%)distilling at l62-l64/0.00l mm.

Uranium penta-npropoxide was also prepared by the exchange reaction.First, 50 cc. (0.183 mole) of uranium pentaethoxide was treated with 70cc. (0.937 mole) of propanol. Upon removal of the solvents anddistillation with a mercury-diffusion pump, 92.7 g. (94.7%) of ura niumpenta-n-propoxide was obtained, and this distilled at 157-159/0.0032 mm.

The corresponding isobutyl compound may be prepared in the same manner.This product is a solid which distilled at 192 C./ 0.007 mm.

Uranium penta-n-butoxide, prepared in accordance with the generalprocedures given for uranium pentaethoxide and uraniumpenta-n-propoxide, distils at 208- 210/ 0.012 mm. The compound is a palebrown liquid which is soluble in all common dry, hydroxyl-free organicsolvents. The compound is sensitive to moisture which effects rapidhydrolysis.

Although the present invention has been described with reference tospecific details of certain embodiments thereof it is not intended thatsuch details shall be regarded as limitations upon the scope of theinvention except so far as included in the following claims.

The foregoing description is for purposes of illustration and since theinvention may be carried out in a variety of forms other than thosespecifically described, it is our intention that the invention be onlylimited by the appended claims or their equivalents.

We claim:

1. As a new composition of matter a compound having the formula U(OR)71where R represents a monovalent alkyl radical having a maximum of fourcarbon atoms and n represents one of the integers selected from thegroup consisting of 4, 5 and 6.

2. As a new composition of matter, uranium tetraalkoxide having amaximum total of sixteen carbon atoms per molecule.

3. As a new composition of matter, uranium pentaalkoxide having amaximum total of twenty carbon atoms per molecule.

4. As a new composition of matter, uranium hexaalkoxide having a maximumtotal of twenty-four carbons per molecule.

5. A method of preparing a uranium hexa-alkoxide which comprisesreacting a uranium penta-alkoxide having the formula U(OR)5, in whichthe OR represents an alkoxy radical having not more than four carbonatoms, with a corresponding alkali alkoxide in which the alkoxy radicalhas the same number of carbon atoms as the alkoxy radical in saiduranium penta-alkoxide under substantially anhydrous conditions to forman alkali uranium hexa-alkoxide addition compound, and then oxidizingsaid addition compound under substantially anhydrous conditions.

6. A method of preparing uranium hexaethoxide which comprises reactinguranium pentaethoxide with an alkali ethoxide under substantiallyanhydrous conditions to form the alkali uranium hexaethoxide additioncompound and then oxidizing said addition compound under substantiallyanhydrous conditions.

7. A step in the method of preparing uranium hexaethoxide comprisingreacting uranium pentaethoxide with an alkali ethoxide undersubstantially anhydrous conditions to form the alkali uraniumhexaethoxide addition compound.

8. A method of preparing a uranium penta-alkoxide which comprisesreacting a uranium tetrahalide with a solution of an alkali metal in amonohydric alcohol having not more than four carbon atoms and undersubstantially anhydrous conditions and after the reaction issubstantially completed oxidizing the solution under substantiallyanhydrous conditions.

9. A method of preparing uranium pentaethoxide Whichcomprises reacting auranium tetrahalide with a solution of an alkali metal in ethanol undersubstantially anhydrous conditions and after the reaction issubstantially completed oxidizing the solution under substantiallyanhydrous conditions.

10. A method of preparing uranium penta-ethoxide which comprisesreacting a uranium tetrahalide with a solution of an alkali metal inethanol and under substantially anhydrous conditions, oxidizing theresultant mixture under substantially anhydrous conditions, and distil-'37 ling off the ethanol first under an inertatmosphereand subsequentlyunder a vacuum.

11. A method of preparing uranium pentaethoxide which comprises reactinga .uranium tetrahalide=with a -17., As.a..new composition ofmatteruranium hexafii-hoxide.

,,18.'A..methodof producing uranium. pentaethoxide which comprisesoxidizing uranium tetraethoxide under solution of an alkali metalinethanol under. substantially substantially anhydrous conditions.

anhydrous conditions, oxidizing the resultant mixture undersubstantially anhydrous conditions, removing the ethanol from thereaction mixture and-subsequently purifying the pentaethoxide bydistillation undera vacuum.

12. A method of preparing uranium hexaethoxidelO which comprisesreacting uranium pentaethoxide with an alkali ethoxide in ethanol undersubstantially anhydrous conditions to form an addition compound,oxidizing the addition compound under substantiallyanhydrous conditions,removing the alcohol from the reaction mixture, .15

and subsequently purifying the product by fractionatingat a lowpressure.

13. A method of forming uranium hexaethoxide which comprises reactinguranium pentaethoxide with an alkali ethoxide in ethanol under an inertatmosphere to form an alkali uranium hexaethoxide addition compound,

reacting said addition compound with a carboxylic peroxide undersubstantially anhydrous conditions to remove the alkali metal therefrom,distilling off said ethanol and subsequently purifying the product byfractionating at a v low pressure. p

14. A method of forming uranium hexaethoxide which comprises reactinguranium pentaethoxidev with sodium ethoxide in ethanol under an inertatmosphere to form the sodium uranium hexaethoxide addition compound,reacting said addition compound withbenzoyl peroxide under substantiallyanhydrous conditions, distilling off said ethanol and subsequentlypurifying the product by fractionating at a low pressure.

15. As a-new composition of matter uranium tetraethoxide.

16. As a new composition of matter uranium pentaethoxide.

19. A method of producing uranium hexaethoxide which comprises oxidizingan alkali metal uranium hexaethoxide under substantially anhydrousconditions.

20. The method of preparing a uranium hexa-alkoxide, which comprisesreacting under substantially anhydrous conditions a uranium tetrahalidewith an alkali metal alkoxide-having not, more than four carbonatoms,then subjecting the reaction mixture to oxidation-with a car-.boxylieperoxide under substantially anhydrous conditions whereby auranium penta-alkoxide is-formed, treating under substantiallyanhydrousconditions said uranium 'penta-alkoxide-with. an alkali metal alkoxidehaving the same nu mber of, carbon atoms as the alkoxide of the uraniumpenta-alkoxide to form an alkali metal uranium .hexa-alkoxide additioncompound, and then oxidizing said addition compound under substantiallyanhydrous conditions.

References Cited in the file of this patent UNITED STATES PATENTS2,125,961 Shoemaker Aug. 9, 1938 OTHER REFERENCES -Friend: Textbook .ofInorganic Chemistry, vol. VII, part III, Chromium and Its Congeners,page 3 (1927), pub. by Charles Grifiin;& Co., Ltd., London.

LiebigsAnnalen, vol. 476 (1929), pages 121, 139, 141, 146, Meerweinetal.

Thiessen et al.: Zeitschrift fiir Anorganische Chemie, vol. 181 (1929),page 292.

Deming: General Chemistry, 3rd ed., page 344 (1930), pub. by John Wiley& Sons, N. Y.

1. AS A NEW COMPOSITION OF MATTER A COMPOUND HAVING THE FORMULA U(OR)NWHERE R REPRESENTS A MONOVALENT ALKYL RADICAL HAVING A MIXIMUM OF FOURCARBON ATOMS AND N REPRESENTS ONE OF THE INTEGERS SELECTED FROM THEGROUP CONSISTING OF 4, 5 AND 6.